DESCRIPTION: (Taken from the application) Mechanical factors play significant and essential roles in modulating chondrocyte metabolic and biosynthetic activities. In articular cartilage, chondrocytes experience a variety of mechano-electrochemical stimuli to which they respond by altering their biosynthetic activities. The magnitude and frequencies of the applied mechanical forces are important factors which govern how the cells respond. Upon compression, the cells experience a combination of strains, pressures, fluid flow, and associated electrokinetic phenomena. Recent literature data suggest that electrokinetic forces may have greater roles in modulating chondrocyte biosynthetic activities in response to dynamic compression. Despite these and other insights gained from studies both in vitro and in vivo, relatively little is known about how chondrocytes sense and transduce extracellular mechanical signals into an ultimate physiologic or biosynthetic response. The primary goal of the current proposal is therefore to investigate the mechanisms through which fluid flow-associated mechano-electrochemical signals are transduced in articular chondrocytes. We hypothesize that: 1) Of the mechano-mechanoelectrical stimuli associated with fluid flow, shear stress rather than shear rate, flow velocity or electrokinetic phenomena, is the predominant modulator of chondrocyte activities; 2) chondrocytes sense and respond to transient flow initiation and steady-state flow conditions via independent mechanochemical transduction pathways; and 3) biochemical factors (e.g., growth factors, cytokines) modulate the response of chondrocytes to mechano-electrical stimuli. The specific aims designed to test these hypotheses are as follows: 1) Determine the effects of fluid-induced shear stress on activation of mitogen-activated protein kinases (MAPKs) and intracellular Ca2+ levels under conditions which delineate the roles of shear rate, flow velocity (e.g., convective transport) and electrokinetic phenomena (normal and altered concomitant streaming potential and streaming current); 2) Perform flow studies examining the effects of different flow onset rates on the Ca2+ and MAPK activation response in articular chondrocytes; 3) Determine the chondrocyte response to flow-induced stimuli in the presence of biochemical factors such as cytokines, serum growth factors, and flow-stimulated cell-conditioned media; and 4) Determine the chondrocyte biosynthetic activities in response to the fluid-induced stimuli quantified in Specific Aims 1 and 2. Successful completion of these studies will greatly enhance our knowledge of mechanotransduction in chondrocytes and contribute to the design of devices and procedures for the development of tissue-engineered cartilage substitutes.